This invention relates generally to a system for determining the specific gravity of a liquid and more particularly to a system useful for continually monitoring the specific gravity of a flowing liquid, e.g. urine, discharged from a catheterized patient.
It is well known that the specific gravity of urine constitutes a significant indicator of kidney function and it is accordingly a common hospital practice to periodically check the specific gravity of a patient's urine output. This is typically done by a nurse placing a urine sample on the measurement surface of a clinical refractometer and then sighting, through an eyepiece, the position of a light/dark boundary line projected onto a graduated scale. Such clinical refractometers are well known and readily commercially available; e.g. (1) American Optical Corporation TS Meter and (2) Schuco Model 5711-2020. Alternatively, the specific gravity of a liquid can be automatically measured by pouring a quantity into a Biovation refractometer of the type disclosed in U.S. Pat. No. 4,381,895.
Apparatus is also well known for continually measuring the amount of urine discharged by a catheterized patient and for displaying urine discharge volume and flow rate via a digital electronic display. As an example, one such apparatus comprises the Vitalmetrics, Inc. Model 210 Urine Monitoring System. Related apparatus is disclosed in U.S. Pat. No. 4,448,207 issued May 15, 1984 and U.S. Pat. No. 4,658,834 issued Apr. 21, 1987. Such apparatus is characterized by a disposable container used to collect discharged urine and a microprocessor based measuring means bacteriologically isolated from the urine.